1. Field of the Invention
The present invention relates to drill pipe safety valves used for capping oil field drill pipe when a blowout occurs through the pipe and, more particularly, to a hydraulicly and mechanically actuated apparatus for automatically positioning the safety valve over the drill pipe and threading the safety valve into the drill pipe.
2. Description of the Related Art
During the drilling of an oil well, the drill bit occasionally penetrates an earth formation that has an unexpectedly high pressure. When the pressure is sufficiently high, the hydrostatic head of drill mud standing in the well is not sufficient to prevent formation fluids from entering the bore hole and traveling upward toward the surface. If such flow is not controlled quickly, a "blowout" of the well occurs and creates very serious safety hazards for personnel working on and around the drilling rig. Further, resulting fire can cause tremendous damage to the drilling equipment.
At a first indication of possible blowout conditions, blowout preventers can be closed around the drill pipe to seal off the annulus. If a kelly by which the drill pipe is driven happens to be attached to the upper end of the string of drill pipe at the time of the potential blowout, then a valve may be present in the system which can be closed to shut off upward flow through the drill pipe itself. However, should upward flow begin while the kelly is not connected to the drill pipe, for example while a threaded connection between pipe sections is being made, a very hazardous situation is presented.
U.S. Pat No. 4,026,354, issued May 31, 1977, shows a somewhat massive device that is lowered over the open end of the pipe by a crane or a boom and operated by a long drive shaft that extends through a kill line to make a connection with the pipe and enable a shut-off valve to be closed. Due to its massive nature, this device cannot be positioned and put into operation as quickly as would obviously be desirable under the circumstances.
U.S. Pat. No. 3,625,282 issued Dec. 7 1971 shows device having a clamp that mates only with a special type of groove arrangement on the upper end of the casing. The clamp has bolt holes that can be aligned with matching holes on the lower flange of a spool where a master valve is mounted. The clamp and spool have an offset hinge bolt to enable the spool to be pivoted into position. However, this apparatus requires the construction of numerous bolts before complete attachment can be accomplished. This is, of course, time-consuming and, thus, potentially dangerous. Further, the clamp assembly is designed for attachment only to a specific type of machined end fitting.
U.S. Pat. No. 4,442,892, issued Apr. 17, 1984, shows an apparatus for stabbing and threading a safety valve into a well pipe. The apparatus includes a tubular canister rotatably mounted on a carriage assembly that is slidably mounted on an upstanding frame. The lower end of the frame has a swivel mounting to a bracket that is attached to the side of an elevator type clamp by which the apparatus is clamped onto the upper end portion of the pipe. After the apparatus is clamped onto the pipe, the operator manually operates a gear drive so as to swivel the apparatus in position over the pipe. With the canister pivoted into position over the pipe, the operator manually operates a second gear drive to cause the canister to be rotated and simultaneously lowered toward the pipe whereby a safety valve mounted inside the canister is automatically threaded into the upper end of the pipe and can be closed to shut off upward flow. While the apparatus is generally satisfactory in operation, the gear drives are relatively complex mechanical devices and, therefore, expensive to manufacture and difficult to assemble.
The present invention is directed to overcoming one or more of the problems set forth above.